As a conventional stabilizer, stabilizers described in JP 2001-506560A and JPH11-510761A are known. For example, in JP 2001-506560A, a torsion bar of U-shape having integrally formed horizontal arms is described. The horizontal torsion bar is provided corresponding to each of a front axle and a rear axle. The front horizontal torsion bar is relatively rotatably connected to an underbody. One end and the other end of the front horizontal torsion bar are connected to the front axle through a drop link and a front cylinder respectively. Thus, a roll posture control mechanism of the front axle is configured. Similarly, the rear horizontal torsion bar is relatively rotatably connected to the underbody. One end and the other end of the rear horizontal torsion bar are connected to the rear axle through a drop link and a rear cylinder. Thus, a roll posture control mechanism of the rear axle is configured. Then, upper chambers of the front cylinder and the rear cylinder are hydraulically connected each other by an upper hydraulic communication tube. Further, lower chambers of the front cylinder and the rear cylinder are hydraulically connected each other by a lower hydraulic communication tube. Thus, a roll moment reaction system, in which roll mode or joint motion mode of the axle motion is responsively applied, is configured.
In the configuration described above, for example, when roll moment occurs at the vehicle, the roll moment is applied to the front cylinder and the rear cylinder in a direction of compression. However, because the front and rear cylinders are hydraulically connected each other so that a hydraulic fluid can transfer therebetween, the cylinders are not compressed by effect of fluid pressure.
However, in the configuration described above, in a situation that roll moment occurs at the vehicle while the vehicle is turning, and that the roll moment is applied to both of the front cylinder and the rear cylinder in a direction of compression, for example, when balance between loads applied to both cylinders is influenced from surface condition of a road on which the vehicle is running or the like, the hydraulic fluid transfers between the cylinders through the upper hydraulic communication tube and the lower hydraulic communication tube. As a result, posture control of the vehicle in relation to roll becomes difficult.
Accordingly, in the situation described above, it is preferable that means for prohibiting hydraulic fluid from flowing between the front cylinder and the rear cylinder is provided. For example, the inventor of the present invention suggests to provide poppet type solenoid valves in the upper hydraulic communication tube and the lower hydraulic communication tube which selectively open and close the upper hydraulic communication tube and the lower hydraulic communication tube.
Here, in respect of cross sectional areas, cross sectional areas of the upper hydraulic communication tube and the lower hydraulic communication tube serving as a hydraulic communication path hydraulically connecting the front cylinder and the rear cylinder are set larger than that of a general fluid pressure system (such as a brake system of a vehicle) corresponding to required amount of flow of the hydraulic fluid. Accordingly, for directly opening and closing the upper hydraulic communication tube and the lower hydraulic communication tube having such a large cross sectional area utilizing such poppet type solenoid valve, a large solenoid that can generate larger electromagnetic force is required. Accordingly, it is difficult to prevent that the valve and overall system including the valve become larger.
A need thus exists for a fluid pressure control apparatus for stabilizers enabling further downsizing of the fluid pressure control apparatus for the stabilizers.